Synthesis and Structural Characterization of the First Lanthanide(II) Cuboidal Cluster. Unexpected C−O Activation by an Unchanged Ytterbium(II) Center

The two new sterically demanding secondary phosphines (C 6 H 4 -2-OMe)RPH ( 1a ) and (C 6 H 3 -2-OMe-3-Me)RPH ( 1b ) [R = CH(SiMe 3 ) 2 ] are synthesized by the reaction of RPCl 2 with 1 equiv of LiC 6 H 4 -2-OMe or LiC 6 H 3 -2-OMe-3-Me, respectively, followed by in situ reduction with LiAlH 4 . Metalation of 1 with Bu n Li, followed by metathesis with KOBu t, yields the potassium salts K{PR(C 6 H 4 -2-OMe)} ( 2a ) and K{PR(C 6 H 3 -2-OMe-3-Me)} ( 2b ). The reaction of K{PR(C 6 H 3 -2-OMe-3-Me)} with YbI 2 yields the diphosphide complex [Yb II {PR(C 6 H 3 -2-OMe-3-Me)} 2 (THF) 2 ] ( 3 ), in which the phosphides act as P, O -chelating ligands. In contrast, reaction of K{PR(C 6 H 4 -2-OMe)} with YbI 2 under similar conditions yields the unexpected alkoxophosphide complex [Yb II {PR(C 6 H 4 -2-O)}(THF)] 4 ·4Et 2 O ( 4 ), via an unusual ligand cleavage reaction involving the transfer of a methyl group from oxygen to phosphorus. Compounds 1 − 4 have been characterized by elemental analyses and multinuclear NMR spectroscopy and compounds 3 and 4 by X-ray crystallography. Compound 3 is monomeric in the solid state, with a distorted all- trans -octahedral geometry about the Yb center; compound 4 crystallizes as an unprecedented tetrameric cluster containing a Yb 4 O 4 cuboidal core. Multi-element NMR spectroscopy suggests that 4 maintains an oligomeric structure in THF solution. The P-containing side product formed in the synthesis of 4 has been isolated and identified as (Me)PR(C 6 H 4 -2-OMe) by comparison of its NMR and mass spectra with those of an authentic sample.